I have a Trek 4500 I've been riding for a couple months now. It was used when I got it...not sure of the exact here. It has a little wear and some components show it, but overall it's a very solid bike.

I went for a ride yesterday and immediately could tell something was up. The steering feels "loose". Where I used to be able to use one hand and control the bike comfortably, it now wants to turn left or right very hard and very suddenly.

Interested and wanting learn bike mechanics anyway, I took the fork loose from the frame, cleaned it, etc. There are some washers and metal rings that go on underneath the handle bars. The bottom one, I believe, is missing a washer of some sort. The handle bars are not completely pushing those metal rings down and keeping the fork sturdy.

I have no idea, though, since I just noticed and the only thing I can conclude is that something should be there but isn't, since all other parts look fine.

Would I just take the bike to a bike shop? Could I possibly get a metal washer or rubber bushing from Lowes? I mean, I'm just a little confused at how I go about replacing the part.

I would like to learn as much as possible by doing it on my own, if that's an option in this case.